The Effects of Stream Crossings on Total Suspended Sediment in North Carolina Piedmont Forests

This study determined total suspended sediment (TSS) at six stream crossings that represented a range of site conditions and forest operations in the Piedmont of North Carolina. Two wood and three steel bridgemats and one culvert were installed to cross the streams. The road classes for the crossings included four temporary skid trails and two permanent forest haul roads. Baseflow and stormflow water samples and continuous stream discharge were measured using the upstream-downstream approach to determine the effects of stream crossings on TSS concentrations and loads. Upstream and downstream TSS concentrations from grab samples were not significantly different at any site during the study period. Baseflow TSS concentrations averaged 21.7 mg/l upstream and 21.1 mg/l downstream across study sites and periods. Stormflow TSS concentrations averaged 84.8 mg/l upstream and 84.7 mg/l downstream across all sites and periods. TSS loads were also comparable to exports from unharvested Piedmont watersheds and other stream crossing studies that used forestry best management practices (BMPs) to protect water quality, averaging 82 kg/ha/year upstream and 80 kg/ha/year downstream of the crossing. Our results add to the body of research indicating that stream crossing BMPs designed in mountain systems can be effectively applied to other regions to protect water quality.